Many important basic chemicals which are utilized in modern society are produced by electrolysis. Nearly all of the chlorine and caustic used in the world today is produced by the electrolysis of aqueous sodium chloride solutions. There is increasing interest in the electrolysis of water for the production of oxygen and, particularly, hydrogen which is finding ever increasing use in our society. Other uses of electrolysis include electroorganic synthesis, batteries and the like and even more common applications such as water purification systems and swimming pool chlorinators.
The so-called flowing mercury cathode cells and diaphragm cells have provided the bulk of the electrolytic production of chlorine and caustic. In more recent times, the membrane-type electrolytic cell has gained popularity because of its ease of operation and, particularly, its lack of polluting effluents such as mercury or the use of carcinogenic material such as asbestos. Membrane-type electrolytic cells generally comprise an anode chamber and a cathode chamber which are defined on their common side by an hydraulically impermeable ion exchange membrane, several types of which are now commercially available but are generally fluorinated polymeric materials which have surface modifications necessary to perform the ion exchange function.
Membrane-type electrolysis cells generally comprise one of two distinct types, that is, the monopolar-type in which the electrodes of each cell are directly connected to a source of power supply, or the bipolar-type in which adjoining cells in a cell bank have a common electrode assembly therebetween which electrode assembly is cathodic on one side and anodic on the other.
Several designs of both monopolar and bipolar membrane cells incorporate a pair of formed metal pan structures which define the anode and cathode compartments when similar pans are assembled in a facing relationship with a membrane interposed therebetween. Cells of this type are described in U.S. Pat. Nos. 4,017,375 and 4,108,752.
Because of the rigorous corrosive conditions existing in the electrolytes of both anode and cathode chambers, it has been necessary to form the cathode and anode pan out of material which is resistant to the electrolyte. In most cases, anode pans were formed from titanium or other valve metal or their alloys in sheet form. Similarly, cathode pans were formed from ferrous metals such as steel, stainless steel and the like. Neither of these materials would be termed good or excellent conductors of electricity and, thus, cell voltages which are high enough to overcome the ohmic resistance of such pans, particularly with respect to titanium, are not as good as a cell which could utilize good electrical conductors such as copper or aluminum in at least a portion of their structure.
A bimetallic iron/titanium separator wall for cathode and anode sides of a bipolar electrode is described in U.S. Pat. No. 4,111,779, Seko et al. While some economies of structure are realized, this design employs metals which are not highly conductive and ohmic losses through the structure are relatively high. Further, atomic hydrogen formed at the cathode can migrate through the iron to the titanium and cause embrittlement and eventual failure thereof.
Further, pans designed in accordance with the teachings of the prior art, such as the above-mentioned U.S. Patents, employ conductor bars which are attached to the rear of the interior of the pan surfaces and which extend toward the separator and upon which the anode and cathode screens are attached. The ohmic resistance loses from these additional electrolyte-resistant materials are apparent.
The utilization of titanium and steel for anolyte and catholyte chambers results in a relatively heavy structure which requires both a substantial support structure in the assembly of these components and heavyweight handling equipment for moving such components when disassembly and assembly become necessary.
It is therefore a principal object of this invention to reduce the ohmic loss in membrane cell structures by forming such structure from a material which is both resistant to the electrolyte where it is in contact therewith and offers lower overall electrical resistance to the flow of current than materials used previously.
It is a further object of this invention to utilize a structure for membrane cells which is both light in weight and conserving of materials utilized in its assembly.
These and other objects of the invention will become apparent to those skilled in the art upon the reading and understanding of this specification.